Fuel price discussion thread (was ‘chaos’)

[jpaul]

My petrol 1.6l turbo Volvo is most fuel efficient in 6th gear about 55/60mph it'll do 50+mpg which is insane really.

which is it 55 or 60 ? aerodynamic give exponential increase in propulsion power needed with speed

@Cambridgeshire people will do 65 on a 3 mile nsl section from 30mph town to my home village, if it was set to 40mph they'd loose a couple of minutes of their lives,
they also typically have to brake at the two bends which their suv's won't navigate at that speed.

I need a provocative rear window sticker that extols driving with an eye on economy.

 

[Rroff]

Top speed doesn't affect fuel consumption much anyway, I mean pushing past 60/70 yes, but most cars are the most fuel efficient in whatever the highest gear is at low RPM.

My petrol 1.6l turbo Volvo is most fuel efficient in 6th gear about 55/60mph it'll do 50+mpg which is insane really.

Hard acceleration is what does it, also not driving smoothly, leaving braking distance so you don't have to stop and start, but rather only slow down a bit.

Out of curiosity and because of this fuel thing I decided to see what I could do, on a tank with my normal driving, I get between 350-380 miles, this tank I got 550 miles, mainly because of very light acceleration and changing up through the gears at low rpm.

So an absolutely massive difference.

I wouldn't say I was necessarily driving much slower though overall.

Getting meaningful economy increases in the real world is 100% about driving approach - being able to sustain momentum, avoiding hard acceleration, etc.

Some of those talked about MPH changes make no sense to me either - the difference between 20 and 30 MPH seems great until you look at the full range of actual data - if you back off a little from 30 the emissions and fuel economy doesn't change much, if you back off a little from 20 a lot of vehicles become exceedingly poor very quickly and the optimal point depends on vehicle - while many common vehicles it peaks around 20 some of the worst polluting vehicles are almost twice as bad at ~18.

 

[MagicBoy]

been mentioned before - if Boris is looking for ways to help people reduce energy costs then a mandated reduction in speed limits wouldn't be a bad thing demand would drop and prices,
to the benefit of those less well off.

Guessing you've not ventured out on a major motorway recently? Bits of the M6, M5 and M4 I've used in the last few weeks around major cities have had 50/60 limits on them "to reduce air pollution".

Prices are taking the proverbial. OPEC and the oil companies are limiting supply to keep the price high and protect their revenue stream. They got spooked when the price went negative during the pandemic. Cartels doing cartel things.

 

[BUDFORCE]

Just did some testing, I needed to nip out for something anyway, reasonably
long straight flat roads (fens are great for this) using cruise control 6th gear.

Very little in it between 50-65 mph.

Was better at 50 than 65, but talking an mpg range of between about 52-55 mpg at those speeds.

That's constant speed though, doesn't factor in the mpg needed to accelerate up to those speeds in the first place, so I guess the above figures are a little misleading, but the point is once you've achieved that speed, there is little difference in maintaining, so on long A roads/motorways with little traffic where you can maintain for longer periods of time this becomes more relevant.

Obviously that's specific to my car.

 

[Rroff]

I dunno about emissions but I do a lot of the same journeys consistently and had a play with it using OBD data awhile back and there was no real meaningful difference in any of the vehicles I drive speed wise, while driving smoothly and keeping momentum made a noticeable albeit not massive difference - especially stuff like slowing into light changes rather than braking and accelerating, etc. (actually annoys me a bit that the lights on my main route home default to red at night - if you drive up to them and stop waiting the change and then set off again it is over 0.3MPG difference over the journey compared to slowing on approach and timing the change, and probably quite bad emissions wise).

Was also interesting that if I got stuck behind a cyclist or something else very slow the fuel economy would drop ridiculously through that bit - way more than I expected.

 

[Simon]

SUL up to €2.20

**** this

This is daylight robbery now. Oil companies are making record profits and the price of petrol is DOUBLE what it was 2 years ago (albeit at the height of lockdown). Total ******* ********. *****.

And oil price is far more than double what it was. Reminder: oil companies operate beyond home borders.

 

[Simon]

I dunno about emissions but I do a lot of the same journeys consistently and had a play with it using OBD data awhile back and there was no real meaningful difference in any of the vehicles I drive speed wise, while driving smoothly and keeping momentum made a noticeable albeit not massive difference - especially stuff like slowing into light changes rather than braking and accelerating, etc.

Was also interesting that if I got stuck behind a cyclist or something else very slow the fuel economy would drop ridiculously through that bit - way more than I expected.

50mph vs 70mph is a massive difference fuel consumption

Probably 20-25% less at 50

 

[mjt]

And oil price is far more than double what it was. Reminder: oil companies operate beyond home borders.

Of course. Governments could be doing more though. I'm not talking about the UK, but in general. If they really wanted to, they could do more to reduce the cost of fuel.

Also - and probably more relevant - OPEC can **** off and all.

 

[Blackjack Davy]

Local and biggest Shell now want £1.71.9 for standard unleaded. I got Sainsbury’s Super in Edinburgh for 1.66.9. Ridiculous pricing.

E10? It amazes me how prices vary so much across the country but sainsburys is usually cheapest it was £1.59 until last tuesday and I got there too late, next day it was £1.61 but thats still cheaper than Shell at £1.67 which is usually amongst the higher priced, wonder how high it'll go this time didn't help I had a massive diversion yesterday due to to police closing the main road and roadworks closing the other

 

[Rroff]

50mph vs 70mph is a massive difference fuel consumption

Probably 20-25% less at 50

I've seen the science - but I'm struggling to see it in the real world. Albeit I tend to drive larger vehicles - vans, pickups and SUVs these days vs smaller petrol engine cars, etc. where maybe it works more like that.

 

[Simon]

Of course. Governments could be doing more though. I'm not talking about the UK, but in general. If they really wanted to, they could do more to reduce the cost of fuel.

Also - and probably more relevant - OPEC can **** off and all.

Well Malaysia subsidise rather than invest in public transport. But it’s rather short term approach to take.

If only there was an alternative energy for cars

 

[Simon]

I've seen the science - but I'm struggling to see it in the real world. Albeit I tend to drive larger vehicles - vans, pickups and SUVs these days vs smaller petrol engine cars, etc. where maybe it works more like that.

Well the aero drag squares as speed increases so it’s probably more relevant on bigger vehicles.

My M3 does 30mph at 50mph. (M4 speed limit) but 25-26mpg at 70mph for example.

EVs see similar, infact they are more impacted by extra speed due to many reasons

 

[Simon]

UK pump prices

The table below shows the latest average petrol and diesel pump prices for the UK and gives a breakdown of how the price is derived. The wholesale prices (as at

www.racfoundation.org

Bio content is expensive based on 10% and 7%. Tax is the killer. Even after the 5p cut.

 

[Rroff]

Well the aero drag squares as speed increases so it’s probably more relevant on bigger vehicles.

My M3 does 30mph at 50mph. (M4 speed limit) but 25-26mpg at 70mph for example.

EVs see similar, infact they are more impacted by extra speed due to many reasons

I'm just not seeing it - I do quite a bit of sticking to 50 MPH on NSL main roads then faster speeds on dual/motorway due to driving vans/pickup and I always get better fuel economy (not by any significant amount though) on the dual/motorway even with a clear run on good roads for both sections. It is only if I'm putting my foot down >70 it quickly starts to hit the economy or getting stuck behind slow moving vehicles.

My pickup the optimal point is getting up to around 66-67MPH and sitting there (which is pretty much lowest RPM in top gear) - it quickly drops off either side of that for highway speeds.

 

[MagicBoy]

I've seen the science - but I'm struggling to see it in the real world. Albeit I tend to drive larger vehicles - vans, pickups and SUVs these days vs smaller petrol engine cars, etc. where maybe it works more like that.

Yeah it's down to aerodynamic drag. So van, pickups and SUVs are going to generate more aerodynamic drag than a "normal car' at 50mph. I'd expect they their optimum efficiency is at at a lower speed.

 

[MagicBoy]

UK pump prices

The table below shows the latest average petrol and diesel pump prices for the UK and gives a breakdown of how the price is derived. The wholesale prices (as at

www.racfoundation.org

Bio content is expensive based on 10% and 7%. Tax is the killer. Even after the 5p cut.

Charging VAT on the pump price which includes the excise duty is a double whammy, although only the base oil price is increasing. With all the inflationary pressures, Gov are raking in the VAT.

 

[Rroff]

Yeah it's down to aerodynamic drag. So van, pickups and SUVs are going to generate more aerodynamic drag than a "normal car' at 50mph. I'd expect they their optimum efficiency is at at a lower speed.

Generally getting stuck behind someone doing 40 in a NSL doesn't do great things to my fuel economy either - albeit they are often driving somewhat erratically causing additional braking/accelerating trying to follow them.

If we are really going to reduce fuel consumption and improve fuel economy in a meaningful way in the real world we need to get more people off the road, including working from home where possible LOL... and improve cycling, etc. infrastructure significantly to both encourage more people out of cars and reduce the amount the mix of traffic is causing additional erosion of fuel efficiency/emissions.

 

[MagicBoy]

Might be something to be said for route planning.

I've started taking the road route to some places nowadays. Driving a hybrid, I get more benefit at urban speeds. When drive the 25+ miles to see Mum I'll get 65mpg wafting through Cheshire on the A-roads. If I take the bypass with all its roundabouts and short 70mph sections between them, I'll get 50mpg and save 5 minutes off a 40 minute journey.

Did a trip to Silverstone the other weekend. On the way back there's 30 minutes of roadworks on the M6, and a closure on the M1 due to an accident. Two choices - let the Sat Nav reroute, or pay £LOL for the M6 Toll. Went with the first option. Sat Nav reroutes me down a 60 limit A-road for about 20 miles to bypass the M6 issues. Added less than 5 minutes despite going through a couple of towns on the way, plus an extra couple of mpg.

 

[Greebo]

I'm just not seeing it - I do quite a bit of sticking to 50 MPH on NSL main roads then faster speeds on dual/motorway due to driving vans/pickup and I always get better fuel economy (not by any significant amount though) on the dual/motorway even with a clear run on good roads for both sections. It is only if I'm putting my foot down >70 it quickly starts to hit the economy or getting stuck behind slow moving vehicles.

My pickup the optimal point is getting up to around 66-67MPH and sitting there (which is pretty much lowest RPM in top gear) - it quickly drops off either side of that for highway speeds.

thats the key, Every car has an optimal maximum mpg speed based on its aerodynamics and its top gear. It varies greatly between cars especially with modern cars with 9 gears and perhaps ridiculous long gearing in the top gear. Its really brought home when I am driving an old car like my MGB with 4 gears. At 70mph the engine is running at more than 3,500 rpm. In my 3l bmw , the engine is barely ticking over at less than 1500rpm.

What speed should I drive to get maximum fuel efficiency?

I know that the faster I drive my car the more gas it uses. But on the other hand I'll get to my destination in less time. Is there a "sweet spot" on the speedometer that would give me maximum fuel efficiency? And if so is it different for different car models?

auto.howstuffworks.com

The sweet spot for different cars could be 40mph in one car and 60mph in another.

 

[SDK^]

Slipstream for the economy win, at any speed

But - Should you accelerate to get into the slipstream quicker, or maintain speed and get there slower?!